Functional characterization of soil microbial communities by messenger RNA analysis

As previous chapters have demonstrated, the first molecular studies of soil used gene probe technology (hybridization) to screen for the presence or absence of specific genes in DNA extracted from soil. The ability to detect specific DNA sequences directly from a soil community has since proven to be a useful tool to improve our understanding of particular soil processes. See Chapter 11 for a treatise on soil DNA extraction methods. Even though these studies provided information with respect to the genotype of members of the microbial community, they could not be used to determine if the specific genes detected were actually expressed within that community. Clearly, the presence of specific genes in the soil microbial community provides information on its functional potential, whereas actual soil functioning depends on the expression of those genes. Expression of genes is regulated by many factors, with control of transcriptional initiation being the major point of regulation. Hence, the mere presence of a particular gene does not necessarily imply its expression under the conditions studied.